Wyatt Earp and his family moved to Lamar, Missouri, around 1869.  Nicholas Earp at some point became the Constable for Lamar.  However, on November 17, 1869, Nicholas offered his resignation as Lamar's Constable.  His resignation was accepted and he was immediately appointed to the position of Justice of the Peace.  On the same day, Wyatt Earp, who was only twenty-one years-old, was appointed as Lamar's Constable.  This appears to have been his first known law position.  The following is the oath that Wyatt Earp swore to when he accepted the position of Lamar's Constable:

I, Wyatt S. Earp do solemnly swear that I will to the best of my ability, diligently and faithfully without partiality or prejudice discharge the duties of Constable, within and for Lamar Township Barton County Missouri. [signed] Wyatt S. Earp

    Wyatt Earp gave a $1,000 bond for this position which was filed on November 26, 1869.   He signed the note and his sureties were his father Nicholas Earp, his uncle J.D. Earp, and James Maupin.  Wyatt remained the town Constable when the town incorporated on March 3, 1870.    Wyatt won an election in November 1870 for the constable position, defeating his half brother Newton Earp.  Very little information is known about his activities as Lamar's Constable.  Court records indicate that he did the usual activities that a constable for a small town generally performed.  One article published by the Soutwest Missourian on June 16, 1870, provide an example of Earp's day to day activities:

COME TO GRIEF

One of our citizens had a brother from a distance call to see him on Monday last, and having not seen each other for a long time, they started around town to have a good time, generally.  Taking aboard a good suppluy of "Forty rod," they wandered around until evening when Constable Earp found one of them upon the street incapable of taking care of himself and took him down to a stone building which he has appropriated for use of just such customers.  As Mr. Earp was about turning the key upon his bird, the other came staggering up enquiring for his brother.  Mr. Earp opened the door and slid him in.  Coming up to the square, Mr. Earp met another hard case in the shape of a tramping butcher, who asked Mr. Earp to purchase him a pencil in place of one he alleged Mr. Earp had borrowed of him some time previous.  Mr. Earp enticed him down to the stone building to procure him a pencil, and of course he shared the fate of the other two.  There being a hole in the roof of the building the three caged birds managed to crawl out before morning, and the stranger not liking the reception he met with here, left for parts unknown.  The other two were brought before Esq. Earp and fined $5 and costs, each.  A few more examples, and the town will be better for it.